1. Field of the Invention
The present invention relates to a solid electrolytic capacitor in which a solid electrolyte type capacitor element is mounted on an insulating substrate.
2. Description of Related Art
FIG. 16 is a cross sectional view of a conventional solid electrolytic capacitor. As shown in FIG. 16, the conventional solid electrolytic capacitor has a solid electrolyte type capacitor element 100, an anode terminal 130, and a cathode terminal 140, which are buried in an enclosure resin 120. The capacitor element 100 has a dielectric layer 103 formed on a surface of an anode body 101 in which an anode lead 102 is planted, an electrolyte layer 104 formed on the dielectric layer 103, and a cathode layer 105 formed on the electrolyte layer 104.
The anode terminal 130 includes one end part 131 which is connected to a tip end part 102a of the anode lead 102 electrically, and the cathode terminal 140 includes one end part 141 which is connected to the cathode layer 105 of the capacitor element 100 electrically. Both the anode terminal 130 and the cathode terminal 140 are drawn out from the enclosure resin 120, and are bent along an outer peripheral surface of the enclosure resin 120 to be extended to a lower surface 122 of the enclosure resin 120. Thereby the other end parts 132, 142 of respective terminals 130, 140 are arranged on the lower surface 122 of the enclosure resin 120, and the other end parts 132, 142 form lower surface electrodes of the solid electrolytic capacitor.
In a manufacturing process of the conventional solid electrolytic capacitor, a bending process needs to be performed on the anode terminal 130 and the cathode terminal 140. Because of this, it is necessary that a portion of the enclosure resin 120 intervening between a lower surface of the capacitor element 100 and the lower surface electrodes has a great thickness, and therefore, a space factor of the capacitor element 100 decreases in the conventional solid electrolytic capacitor. Also, because developed lengths of the anode terminal 130 and the cathode terminal 140 are great, lengths of electrically-conducting paths from the capacitor element 100 to the lower surface electrodes are also great, increasing the equivalent series resistance (ESR) or equivalent series inductance (ESL) of the solid electrolytic capacitor.
Therefore, as shown in FIG. 17, there has been proposed to mount the capacitor element 100 on an insulating substrate 150. The insulating substrate 150 includes a first surface 151, on which a first anode layer 161 and a first cathode layer 171 are formed, and the capacitor element 100 is mounted on the first cathode layer 171. Also, the insulating substrate 150 includes a second surface 152 on the opposite side to the first surface 151. On the second surface 152, formed are a second anode layer 162 at a position opposed to the first anode layer 161 through the insulating substrate 150 and a second cathode layer 172 at a position opposed to the first cathode layer 171 through the insulating substrate 150. The second anode layer 162 and the second cathode layer 172 form lower surface electrodes.
The insulating substrate 150 is further provided with an anode via 163 and a cathode via 173 which penetrate the insulating substrate 150 from the first surface 151 to the second surface 152. The anode via 163 connects the first anode layer 161 and the second anode layer 162 to each other electrically, and the cathode via 173 connects the first cathode layer 171 and the second cathode layer 172 to each other electrically.
As shown in FIG. 17, a pad member 110 is placed on a surface of the first anode layer 161, and which is made of metal and has conductive property. A tip end part 102a of the anode lead 102 is connected to a tip end part of the pad member 110. In contrast, the cathode layer 105 of the capacitor element 100 is connected to the first cathode layer 171.
By forming the solid electrolytic capacitor using the insulating substrate 150, distances from the lower surface of the capacitor element 100 to the lower surface electrodes decrease. Therefore, lengths of electrically-conducting paths from the capacitor element 100 to the lower surface electrodes decrease, and the ESR or ESL of the solid electrolytic capacitor decreases.
Also, in the solid electrolytic capacitor shown in FIG. 17, is not necessary to perform the bending process which is required in the manufacturing process of the solid electrolytic capacitor shown in FIG. 16.
However, in the solid electrolytic capacitor shown in FIG. 17, in a case where the tip end part 102a of the anode lead 102 and the tip end part of the metal pad member 110 are connected by welding, a part of the pad member 110 melts, resulting in change in a height dimension of the pad member 110, or positional shift of the pad member 110 due to pressing force applied to the pad member 110 at the time of welding, to possibly deteriorating assembling precision.